The annual New York City ritual to locate new charter schools in public-school buildings has begun — with the usual argument that the co-locations will cause an unbearable space crunch. In fact, the predictions of doom never come true — and a growing body of evidence refutes the “blame co-location” theory of overcrowding.

An Independent Budget Office report this summer found that buildings in which charter schools and traditional public schools share space are less crowded than single-school buildings. The findings were hugely significant because the United Federation of Teachers and the NAACP had spent the spring and early summer in court trying to block co-locations, arguing in part that letting charters move in would result in harmful overcrowding.

Intrigued by the IBO’s results, we at the NYC Charter School Center took the study a step further, analyzing public-school utilization data to see how charter co-locations affected the overall capacity of a school building as well as how individual schools within a building fared. Our findings not only confirmed the IBO’s — buildings in which charter schools share space with district schools are the city’s least crowded — but showed that the charter school typically gets the rawer deal.

While the average utilization rates of single-school buildings in the five boroughs is about 104 percent, buildings in which district and charter schools share space are just 76 percent filled. And the charter-school side of the building tends to be muchmore overcrowded.

In such buildings, the district schools are, on average, at 69 percent capacity, while charter schools are at nearly 110 percent capacity — higher than even the citywide average. Charter students are packed in like sardines.

Even so, charter schools still post strong academic results.

None of this surprises those in charter schools. They’ve seen kindergartners squeezed into the top floor of a five-story school building, elementary students in a building with high-schoolers and charter schools shoved into trailers in a schoolyard.

But you’ll rarely hear charters complain about the quality or quantity of the space they receive, because the alternative is nonexistence. Charters get no public financing for facilities, so many rely on public space.

Indeed, the two reasons the city’s charters have grown from 17 schools in 2002 to 136 today are overwhelming demand from parents and access to space. The city Department of Education’s willingness to provide space has expanded options for families, and it must continue.

If charters aren’t causing overcrowding, then why all the noise? In part, it’s union politics, adult interests and jobs. But it’s also a question of perception: Traditional schools don’t like to lose space they’re used to having. It’s human nature to want to hold on to what you have.

But when you hear these complaints, please remember that even after a charter school has come in, the district schools are still generally much better off than most in terms of space.

Most schools share space well and find ways to work together to benefit all students. A school system in which choice and collaboration can flourish is one that serves children best.